Slow Horses Season 1 Review: The Spies MI5 Would Rather Forget

Official promotional image for Slow Horses Season 1. Apple TV+ promotional material, used for review and commentary.

Adapted from Mick Herron’s first Slough House novel, Apple TV+’s six-episode first season of Slow Horses begins by presenting River Cartwright as the kind of young MI5 agent who normally anchors a spy thriller. He is ambitious, physically capable and racing through an airport during a counterterrorism training exercise that is rapidly going wrong. The sequence appears designed to establish his credentials.

Instead, it ends his career.

River is sent to Slough House, the neglected office where MI5 deposits officers it cannot quite dismiss. Its inhabitants—the “slow horses”—have embarrassed the Service, antagonised the wrong superior, made serious mistakes or simply become professionally inconvenient. They receive tedious assignments in the apparent hope that boredom and humiliation will eventually persuade them to resign.

The cleverness of the premise lies not only in giving disgraced spies another chance, but in asking who gets classified as a failure in the first place. Slough House contains MI5’s visible failures. Season one gradually turns towards the failures committed by people powerful enough to remain at headquarters.

That institutional tension also explains the series’ unusually smooth mixture of investigation, political manoeuvring and action. Investigation establishes what happened. Political manoeuvring determines what can safely be admitted. Action begins when the distance between those two versions can no longer be maintained.

A Modern Spy Thriller with a Cold War Inheritance

Although Slow Horses takes place in contemporary London, much of its atmosphere belongs to an older tradition of British espionage fiction. The streets are grey, the offices are cramped, and information travels through conversations, personal histories, favours and carefully managed leaks. Even as the plot accelerates, the important question is often not simply what happened, but who will control the official account.

The series frequently reminded me of reading John le Carré. The resemblance lies less in any particular plot device than in its understanding of intelligence work as a profession conducted inside institutions rather than above them. National security may provide the justification, but careers, resentments and organisational loyalties shape how people respond when an operation begins to fail.

There is also a trace of Frederick Forsyth in the attention paid to procedure: fragments of intelligence passing between departments, assumptions hardening into operational decisions, and minor details acquiring importance once placed in the correct sequence. Yet Slow Horses is far less reverent towards the profession. It retains the machinery of the traditional spy thriller while stripping away most of its dignity.

Slough House is not the concealed centre of a secret war. It resembles an underfunded government department everyone at headquarters hopes will quietly disappear. Its rooms are shabby, its employees look tired, and its daily work seems designed to extinguish whatever initiative they still possess.

That roughness gives the series much of its personality. As the first Apple TV+ production I had watched, it felt unexpectedly unpolished compared with the heavily lacquered streaming thrillers I had come to expect. That may say more about this particular production than about the platform, but the lack of glamour suits the material. Slough House should not look like an attractively distressed office assembled by a production designer. It should look as though no one with authority has cared about it for years.

River Cartwright and the Uses of Failure

River initially occupies the most familiar position in the story. He believes he has been unfairly condemned for the failed training exercise and assumes that, unlike the others at Slough House, he does not truly belong there. The season complicates that belief without entirely disproving it. The reason for his exile is more interesting than simple incompetence, and the gradual disclosure of what happened provides one of the story’s most satisfying inversions.

The irony is that River continues to supply evidence for the judgement imposed upon him. He is determined, capable and sometimes perceptive, but also impulsive, proud and dangerously eager to prove himself. He enters situations before he fully understands them, mistakes good intentions for sufficient justification and repeatedly creates new problems while trying to correct old ones.

At times, his recklessness becomes an almost too convenient mechanism for pushing the plot forward. It nevertheless prevents him from becoming the conventional wronged hero whose eventual success proves that everyone else was foolish. Institutional injustice and personal fallibility coexist: River has legitimate reasons to feel betrayed, but that betrayal intensifies the impatience that makes him unreliable.

His real problem is therefore more interesting than merely clearing his name. River must decide whether he wants to become a better intelligence officer or simply recover the status he believes was stolen from him. The two ambitions are not necessarily the same.

Jackson Lamb and Diana Taverner: Two Forms of Power

The strongest performances belong to Gary Oldman as Jackson Lamb and Kristin Scott Thomas as Diana Taverner. Both characters are manipulative, ruthless and often horrible. None of that diminishes the pleasure of watching them work.

Lamb drinks, smokes, insults his staff and treats personal hygiene as an ideological compromise. He appears to have turned physical and social unpleasantness into a defensive perimeter. If Slough House is a professional graveyard, Lamb is its malicious caretaker.

Oldman avoids the easy version of the character. Lamb is not a kindly mentor disguised by a few rude remarks. His intelligence does not excuse his conduct, and his occasional loyalty does not make him pleasant. His apparent decay is partly camouflage, though not necessarily a pretence: his appearance encourages people to underestimate him, while his contempt prevents subordinates from expecting reassurance. He often seems to be the least respectable person in the room while understanding the room better than anyone else.

The series also gets considerable comic mileage from Lamb’s refusal to observe contemporary rules of speech. He says something offensive, someone tells him that he cannot say it, and Lamb behaves as though the objection were another tiresome piece of administrative guidance. The joke works because it is less a serious argument about political correctness than a struggle over who controls the conversation. Lamb knows which boundaries he is crossing. Provoking the correction forces everyone else onto ground he has chosen.

At MI5 headquarters, Taverner exercises power through the forms of respectability Lamb has abandoned. She is controlled where he is dishevelled, diplomatic where he is openly insulting and institutionally powerful where he has been pushed to the margins. Yet they understand one another because both know what the Service becomes when an operation goes wrong.

Taverner’s conversations are often more tense than scenes involving weapons. Every instruction contains a secondary negotiation over credit, risk and responsibility. Who will receive recognition if the operation succeeds? Who can be isolated if it fails? Which account of events will remain defensible once ministers, journalists and senior officers begin asking questions?

Thomas plays her without asking the audience to mistake composure for moral restraint. Taverner speaks the language of institutional necessity while treating people as expendable pieces of an operation. She is compelling not because she is secretly sympathetic, but because she understands several levels of the game at once.

Lamb and Taverner represent two forms of institutional survival. Taverner remains at the centre and uses professional decorum as an instrument of power. Lamb has been expelled to the margins and uses indecorum to make himself difficult to manage. Their confrontations work because neither can easily deceive the other about what MI5 is protecting.

Learning How Slough House Works

The first season spends considerable time introducing the other inhabitants of Slough House. There is a faint resemblance to the first season of The Wire, not in scale or depth, but in the way learning how the workplace functions becomes part of learning what the story is about. The difference is that the Slough House team has already been assembled. Its members have simply stopped functioning as a team.

They occupy the same building but share no clear purpose. Most have arrived through some mixture of error, misfortune and institutional politics, and each has adapted differently. Some remain ambitious. Some are bitter. Others have surrendered to boredom or concealed the circumstances of their decline behind sarcasm and routine.

The season’s task is not to bring together a group of specialists, but to reveal what remains of people whom the institution has already classified as useless. Their personalities emerge through office habits, petty conflicts and their responses when apparently meaningless work begins to acquire real consequences.

The six-episode structure imposes limits. Several slow horses remain more legible as workplace types than as fully developed characters, and the season is better at making the office feel inhabited than at making every inhabitant feel indispensable. The comparison with The Wire should not be pushed too far; Slow Horses lacks the space to give its ensemble comparable social or psychological depth.

What it does capture is the strange solidarity of people discarded for different reasons. Slough House is not initially a family, a fellowship or even a functional workplace. It is a collection of damaged professional identities forced into proximity. When its members begin acting with something resembling shared purpose, the change feels earned because the series never reveals them as Britain’s finest hidden agents. They remain compromised; rejection has merely failed to eliminate all their experience, instinct and desire to matter.

Investigation, Politics and Action

The central plot begins with the abduction of Hassan Ahmed, a British-Pakistani student, by a far-right nationalist group calling itself the Sons of Albion. The threat supplies the season with urgency, but the kidnapping is only one part of the story. Slow Horses is equally concerned with how MI5 interprets, exploits and attempts to contain the crisis.

This is where the series occasionally recalls House of Cards at its best. Political manoeuvring is not material placed between action scenes; it is itself a form of action. A conversation in an office can alter the meaning of an operation. An instruction may be operationally plausible, politically useful and morally indefensible at the same time.

Unlike House of Cards, however, Slow Horses is sceptical of mastery. Its schemers are formidable, but their plans deteriorate when they encounter vanity, incompetence, conflicting incentives and chance. The pleasure lies not in watching a perfect strategist control the board, but in watching several intelligent people discover that other human beings refuse to remain pieces.

The investigative, political and physical strands reinforce one another. Clues create political problems. Political decisions distort the investigation. Operational mistakes become weapons in the struggle over responsibility. By the time someone starts running, the reasons for the chase have already been established in offices, archives and private conversations.

The action works because it arrives as consequence rather than spectacle. The characters do not become more competent when weapons appear: River remains impulsive, the slow horses remain imperfectly coordinated, and headquarters remains preoccupied with how events will be interpreted. Physical danger is the point at which institutional decisions become impossible to keep abstract. Excitement does not suspend the political story; it is where that story acquires bodies, distances and deadlines.

The Failures MI5 Can Afford to See

Slough House treats failure not merely as an event but as an administrative identity. Once someone has been placed there, every action is interpreted through the classification. River’s mistakes prove that he belongs. His successes become accidents, inconveniences or evidence that someone else guided him correctly.

The supposedly competent officers at headquarters are hardly free from error. They are simply better positioned to distribute its consequences. Large institutions do not always divide the capable from the incapable. They often divide those whose mistakes can be absorbed, concealed or transferred from those whose mistakes become permanent labels.

That does not make the slow horses misunderstood geniuses. Some have genuinely damaged their careers through bad judgement or destructive behaviour, and River repeatedly demonstrates why unlimited confidence in his instincts would be dangerous. The series does not replace one flattering hierarchy with another.

Professional status nevertheless proves to be an unreliable measure of competence, honesty or usefulness. Slough House contains people whose failures have become part of their official identity. Headquarters contains people with enough authority to determine what counts as failure and whose name will be attached to it.

The shabby offices, political conversations, River’s thwarted ambition, Lamb’s cultivated unpleasantness and Taverner’s polished ruthlessness all belong to the same institutional landscape. Slough House is where MI5 stores the failures it can name. Slow Horses is more interested in the failures it cannot afford to acknowledge.